Welcome to Pharo community, Irfan.
You should take a look at Zinc framework. Here is a very nice documentation, you should be able to solve your problem after reading it.
Also as far as I know there is work in progress on the OAuth protocol, you can take a look here: https://github.com/svenvc/docs/blob/master/zinc/zinc-sso-paper.md. You definitely want to take a look at it because there are also 2 demos where you can interact with twitter